The invention relates to a paging receiver having a receiver section for producing digital data from a received signal and having an evaluation section for evaluating the digital data and having a power supply divider with which at least one power supply to the receiver section can be switched on and off.
A case in which such a paging receiver can be used is a car telephone, in which the paging receiver forms a part of the receiver. In portable versions of a car telephone the batteries required for the power supply have to be carried along. Therefore, power-saving measures which lengthen the useful life of a set of batteries are highly desirable. During transmission there is a relatively high power consumption, but only for the usually short duration of a telephone conversation. In comparison with the power consumption of the receiver the power consumption of the transmitter is comparatively small. As the receiver of the car telephone has to be in operation uninterruptedly for accessibility at any time, because a paging call may come in at any time, even relatively small power savings in the receiver can have a decisive effect on the overall power consumption.
In the European Patent Specification No. 0 092 219 and corresponding U.S. Pat. No. 4,479,261 paging receiver is disclosed, which comprises among other things a receiver section, an evaluation logic and a power supply divider. The receiver section divides into two receiver sub-sets which, independently, can be disconnected from the power supply by the power supply divider, whereas the extent sub-sets remain connected to the power supply. Each receiver sub-set is assigned a timing element.
The individual paging receivers are arranged in groups, one time slot of a time-division multiplex frame being provided for each group. In a time slot a data block is transmitted which, for the selection of a single paging receiver (paging call), contains the address code assigned to this paging receiver.
The receiver sub-sets, after receiving the beginning of the data block, remain connected to the power supply for a preset fixed time interval, called time-on time interval hereinafter. To save energy, the power supply to the receiver sub-sets is interrupted after the time-on time interval has ended for a second time interval, called time-off time interval hereinafter. As no data must be lost for the evaluation of the data block, the time-on time interval mentioned in the above Patent Specification is determined such that it has not finished until the end of the assigned data block. The time-off time interval is determined such, that the receiver section is again fully operative at the beginning of the next assigned time slot. When the timing elements are adjusted, the time delay of the different receiver sub-sets has been taken account of, so that the power supplies to the receiver sub-sets are again switched on at different instants, while these instants have a preset value relative to the beginning of the time slots. This subdivision avoids the time-on interval of the power supply to the receiver section having to be adjusted to the receiver sub-set having the largest time delay.
Such a circuit can always be used if between the end of the data block and the beginning of the next interesting data block there is a fixed time interval, which has to exceed the time delay of the receiver sub-set having the largest time delay. If the end and beginning of the data blocks, however, occur in shorter time intervals or immediately after each other, no energy saving can be achieved any longer with the abovedescribed circuit arrangement as the time-off time interval becomes zero.
Therefore, the present invention has for its object to provide a circuit arrangement of the type mentioned in the preamble, in which energy saving is achieved by temporarily switching off sub-sets even if the time interval between the end of a received data block and the beginning of the next data block still to be received is shorter than the time delay of the sub-sets to be switched off for the purpose of the energy saving.